The invention is directed to improvements in fuel injection pumps for internal combustion engines.
In such fuel injection pumps, the pressure plate serves to define the spacing between the tappet and the piston bottom of the pump piston, and optionally also to adjust the supply onset of the fuel injection pump; to reduce wear, the pressure plate is made of highly wear-resistant steel, such as that also used for the pump piston.
In a known fuel injection pump of the above-mentioned type (German Offenlegungsschrift No. 31 28 544), the pressure plate is retained in a centered and positive manner, on the underside of the spring plate facing the tappet, by the pressure spring. If the pump piston should stick in its top dead center position because of some malfunction effecting an attendant lifting of the pump piston tappet, which the cam continues to move back and forth, then the pressure plate may drop out of its centered position on the underside of the spring plate and cause damage to the injection pump.
In another known fuel injection pump (Austrian Pat. No. 201 352), to avoid this threat of damage to the pump, the piston bottom is seated in the pressure plate, which has a recess for this purpose and a cutout for receiving the piston bottom. The top of the pressure plate is widened and serves to replace the spring plate as the bearing surface for the pressure spring.
This kind of pressure plate is not economical to manufacture and thus is not a very suitable spare part, especially where many of various thicknesses, have to be kept on hand to adapt to the varying spacing between the tappet and the piston bottom. In the known fuel injection pump, an additional auxiliary shim has therefore been inserted, with a variable thickness depending on the tolerance that needs to be compensated for, in between the pressure plate and the tappet. This auxiliary shim is embodied as a spring clip, which is introduced into the tappet via a lateral recess that is accessible from the outside; in the inserted state, the spring clip is braced on its circumference on the tappet. This prevents the auxiliary skim from falling out if the pump piston should stick at top dead center. Overall, this known injection pump is of an impractical construction and thus it is difficult to assemble.